Since the publication of "An Account of the Fox Glove and Some of its Medical Uses; with Practical Remarks in Dropsy, and other Diseases" by William Withering over two hundred years ago, the usefulness of digitalis has been in the area of cardiovascular diseases. Whether it is for the control of cardiac arrythmias or for its inotropic effect on the failing heart, the cardiac glycosides have an established role in treating heart disease.
Cardiac glycosides are found in a number of plants, and a few are present in the venom of certain toads. Cardiac glycosides have been found in twelve plant families including the dogbone family (Apocyanaceae), the figwort family (Serophulariaceae) the lily family (Liliaceae), the mulberry family (Moraceae) and the buttercup family (Ranunculaceae). The main source is Digitalis spp. Recently, cardiac glycosides have also been found in insects such as grasshoppers and butterflies which take them up in their vegetable diet. The term "digitalis" as used herein designates the entire group of cardiac glycosides rather than only those obtained from digitalis.